This invention relates to a clamp provided with force applying members adapted to be positioned in encircling relation about the rim of a workpiece, such as a pipe or cylindrical vessel, having a noncircular cross-section to reform the same to a circular cross-section and, in particular, to a clamp which simultaneously expands and/or contracts the force applying members in such a manner that they rotate from a non-engaging first position defining a first circle to a workpiece engaging second position defining a second circle.
Pipe or cylindrical vessel fit-up clamps commonly use a large number of individual adjusting screws each having its axis aligned with a radius extending from a longitudinal axis generally representing the central axial axis of the workpiece. Such an arrangement is shown in U.S. Pat. No. 3,952,936 issued Apr. 27, 1976. Separately adjusting these screws can be very time-consuming and even with great care it may be impossible to get a workpiece truly round. Further, these screws cannot be rapidly reset for another workpiece since the screws must be individually adjusted to a new diameter. As shown in U.S. Pat. No. 4,890,473 issued Jan. 2, 1990, a clamp was subsequently developed that utilized multiple series of force applying members that simultaneously pivot to engage a workpiece, however, this clamp utilized a complicated chain driven worm gear for individually pivoting each series of force applying members into engagement. Although this was an improvement over individually adjusting screws, uniform clamping engagement was still unable to be achieved. Thus, it would be desirable to have a clamp in which all force applying members are actuated simultaneously in unison by a single driving mechanism that is uncomplicated and easily operated and maintained.
In the present invention, the clamp has a frame comprising a pair of rigid stationary rings, each having a circular inside opening defined by a diameter greater than the exterior diameter of the workpiece to be encircled. The clamp also has a plurality of generally equi-angularly spaced, force applying assemblies that are pivotally coupled between the rings and each having a force applying member. The present invention further comprises a novel drive arrangement for simultaneously driving all of the force applying members into and out of forcible engagement with the workpiece. This improved drive arrangement utilizes a unique drive ring, disposed between the pair of stationary rings, that is pivotally coupled to all of the force applying assemblies. The inner radial surface of this drive ring engages with spool shaped rollers, that are located between the force applying assemblies, thereby retaining the drive ring while permitting the drive ring to be axially rotated relative to the stationary rings. Rotating the drive ring causes one end of the force applying assemblies coupled thereto to be displaced, further causing the opposite end of the force applying assemblies to pivot into or out of forcible engagement with the workpiece. Rotation of the drive ring is accomplished by hydraulic actuators which are coupled to the rigid stationary rings at one end and to the drive ring at an opposite end. A hydraulic control system energizes these hydraulic actuators in unison, causing the drive ring to axially rotate, thereby causing the force applying assemblies to be simultaneously pivoted. Thus, the force applying members are simultaneously rotated into or out of forcible engagement with the workpiece, providing for uniform displacement of the force applying members.
An advantage of such a clamp is the ability to achieve roundness in a workpiece to be welded with a minimum of effort but with a maximum diametral accuracy and to accommodate workpieces of different diameters within the range of the clamp.
Another advantage of the clamp having a contracting opening is that a multitude of force applying members can be simultaneously and uniformly adjusted by a single driving means to positions such that each force applying member is always positioned tangent to a circle. Furthermore, this positioning can be controlled with great precision over the entire range of diameters by a hydraulic control system.
Yet another advantage of the present invention is the ease with which all force applying members of the clamp can be simultaneously rotated into and out of engagement with the workpiece by a novel, yet uncomplicated, driving arrangement that is controlled by an easily operated and maintained hydraulic control system.
Additional advantages and features of the present invention will become apparent from the subsequent description and claims taken in conjunction with the accompanying drawings.